The "Macs are too expensive" argument is one of the most tiresome and long-lived flamewars in internet history. Obviously, Apple makes a premium product and charges premium prices, and you can always find a computer from another vendor that seems to match or exceed specs that costs less. But if you look at Apple's Mac Pro line, and compare it not so much to other vendors, but to the past lineup of Mac Pros, you discover some very unpleasant truths that help explain why Apple is enjoying record earnings for their Mac line, but doing so to the detriment of some its most loyal and valuable customers.

That's true, but only relevant once Windows is no longer the dominant 'operating system'.
OSX isn't gonna be ported that fast, either.

Do you really think these multi-billion-dollar code bases are going to be re-written in 10 years? I know they could be, but these companies will not.

I suspect that the question of relevance refers to my statement:

If/when there is a commercially available breakthrough in MM speed ([...]), low-level computer architecture will change dramatically, as will programming techniques.

If so, I don't mean to imply that such upgrades couldn't be largely backward compatible. Most of the architecture changes would be in areas such as the cache management and MMU (i.e., the "northbridge"). Even the OS, other than managing TLBs scarcely touches this; it might even be possible to make these changes wholly invisible; it may be worthwhile to provide some kernel patching, however.

The changes in programming techniques would largely be simplifications; some software needs to be somewhat cache aware to perform adequately; the need for this would largely or entirely go away.

When 64-bit architecture, the "NX" bit, DDR3, multiple CPUs and virtualization technology were each introduced, Windows, OSX and other Operating Systems continued to operate, albeit with patches and upgrades to support new hardware. This could easily be the same type of upgrade -- although I can virtually guarantee that it would require brand new CPU sockets on our motherboards.